table spaces

Performance related question.
With Linux (centos 6.3+), 64bit, ext4 in mind, how would you guys go about
distributing write load across disks.

Lets say I have quite few disks, and I can partition them the way I want,
in mirror configuration (to get some hardware failure resilience). Should I
separate tables from indexes onto separate raids ?

I know WAL has to go on a separate disk, for added performance.

I'm looking for your experiences, and most importantly how do you go about
deciding which way is best. I.e. which combinations make sense to try out
first, short of all permutations :-)

Thanks.

--
GJ